In communications networks, it may be challenging to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.
One component of wireless communications networks where it may be challenging to obtain good performance and capacity is the antennas. For example, in order to perform beam-forming of one or multiple antenna beams/lobes towards desired directions for array antennas, the relative phase of the individual signals feeding the individual antenna ports needs to be controlled.
Such control may be enabled by generating individual electrical signals from individual digital signals, in which case the required phase shift is performed in the digital domain. This is referred to as digital beam-forming.
Alternatively, the individual electrical signals may be generated from a common analogue signal, which is split to the desired number of individual signals needed, followed by individual phase-shift in the analogue domain. This is referred to as analogue beam-forming.
Another option for analogue beam-forming is to use different forms of signal distribution networks. One commonly used implementation is the use of the so-called Butler matrix. In such implementations the signal splitting and phase-shifting is performed in the Butler matrix. Such an implementation may generally also require some additional signal switches in order to perform the selection of different beam directions.
There are also beam-forming architectures that use combinations of analogue and digital phase-shifting; e.g., using digital phase-shifting to control the beam in azimuth (sideways) and analogue phase-shifting to control the beam in elevation.
As the skilled person understands, the above disclosed means for beam-forming have their particular benefits and limitations. In general terms, digital beam-forming may be considered flexible and may support multiple simultaneous beams, but the implementation may be complicated as it requires individual signal conversion between the digital and the analogue domains. Analogue beam-forming may be advantageous from the perspective that it relies on analogue signal processing, which does not need to involve multiple instances of data converters (digital-to-analog converters and analog-to-digital converters) and/or up/down converters. Signal processing is instead accomplished by means of splitting, combing and phase-rotations of analogue signal components. There will naturally be quality aspects to consider for the various parts in the analogue signal processing system, such as gain and phase ripple requirements over the pass-band, signal to noise level, nonlinear distortion effects etc. The analogue beam-forming may commonly be less complicated (such as physically smaller, physically lighter, consuming less power, etc.) than the digital beam-forming, but still a complicated design may be required in order to meet the above mentioned signal quality aspects. Another limitation for the above disclosed analogue beam-forming is that analogue beam-forming inherently only supports a single beam. Providing multiple beams may thus require multiple instances of phase-shifters or, for implementations based on using the Butler matrix, ways to connect multiple analogue signals to multiple inputs of the Butler matrix.
Another aspect of steerable antenna systems is the number of independent antenna ports needed in order to obtain certain performance, such as, but not limited to, antenna beam-width, scanning/deflection angles of the antenna beam, and undesired antenna beams (so-called side-lobes and grating-lobes). In general terms, the higher the number of antenna ports, the better the antenna performance may be controlled. However, using a higher number of elements may commonly require a larger amount of independently controlled signal paths, and associated functions such as amplifiers and up/down-converters (mixers).
For example, distribution networks using a standard form of the well-known 8-by-8 or 16-by-16 Butler Matrix will normally require a high number of components, such as 90-degree hybrid couplers. This tends to make the implementation un-practical considering the physical size and complexity of the distribution network.
Hence, there is still a need for improved distribution networks for antenna arrangements.